1. Field of the Invention
The present invention relates to digital home service and, more particularly, to an effective digital home media distribution apparatus and method for realizing high-quality media streaming in real time through a digital communication network.
2. Description of the Related Art
Recently an interest in digital home service provided using an Internet protocol (IP) network is growing due to a rapid development in the multimedia and network technology. The digital home service provides entertainment service in real time based on digital media contents via high-definition (HD) digital video devices. Thus, it is necessary to provide real-time media services that are capable of distributing seamless and sequential media streams to all digital home media receivers. However, since a QoS (quality-of-service) model of a current IP network employs a best-effort (BE) scheme regardless of service types, the QoS model cannot ensure end-to-end QoS required for the real-time applications in the digital media streaming.
Accordingly, there is a need for a new network to realize real-time and high-quality media streaming in an IP network. In particular, an adaptive media-streaming scheme applicable to a network environment that changes dynamically is required for the IP streaming service. There are various schemes for realizing the network adaptive media streaming, but the schemes may be largely divided into an end-to-end adaptive scheme and an adaptive scheme, which relates network-intermediate nodes according to adaptation positions.
In the end-to-end adaptive scheme, both a transmitter and a receiver take a leading role in a network, wherein the transmission end inserts information for dynamically adjusting the media transmission rate and for coping with a loss environment using the metric information feedback from the reception end. In contrast, the adaptive scheme emphasizes the roles of intermediate nodes serving to distribute media streams, such as a media gateway (MG) and a home gateway (HG).
In addition, while the end-to-end adaptive scheme focuses on the dynamic control of QoS based on streams, the adaptive scheme may be applied to an environment having plural receivers by controlling plural streams based on QoS classes (class-based aggregated QoS mapping). In this case, relatively dynamic adaptive schemes such as proxy/cashing and trans-coding may be employed.
In order to employ the adaptive media-transmission schemes, a metric for representing the end-to-end performance with respect to media transmission must be defined, and then a monitoring scheme for measuring the metric must be performed. Accordingly, to realize HD media streaming for guaranteeing quality of service in digital homes connected to a broadband network, an end-to-end network adaptive transmission technique must be employed together with the adaptive scheme relating to the intermediate nodes for metrics relating to media stream delivery. Therefore, it is necessary to employ an approaching scheme that can stabilize and improve a network-adaptive media delivery framework in accordance with a targeted service and network environment by well-harmonizing interfaces while utilizing elementary techniques in proper combination.
FIG. 1 shows a network adaptive framework for transmission of a moving picture employing the conventional end-to-end adaptive scheme.
As shown, a server 100 at the transmission end performs a relative prioritization scheme based on a temporal scalability of a video. To this end, the server 100 includes a priority packetization unit 110 for performing real-time parsing and prioritized packetization with respect to media streams, a packet dropping unit 120, and an IP streamer 160 for performing scheduling.
In operation, a network monitoring and feedback information reception unit 150 receives feedback information regarding transmission quality between the server and a client 170 from the client 170 and provides feedback information to a forward error correction (FEC) control unit 140. The FEC control unit 140 controls the packet dropping unit 120 and an FEC encoding unit 130 according to the feedback information. The priority packetization unit 110 parses media streams in real time and creates packets having priority. The packet dropping unit 120 removes packets having relatively low priority or bypasses all packets under the control of the FEC control unit 140. The FEC encoding unit 130 receives packets from the packet dropping unit 120 for error correction and encodes the received packets according to a coding rate determined by the FEC control unit 140. The IP streamer 160 adds three-layer and two-layer headers to the encoded packets to create IP packet streams. Thereafter, the IP packet streams are delivered to the client 170.
The server 100 provides media streams with a transmission rate suitable for a current network condition and also provides a receiver condition by adjusting a frame transmission rate of a video stream occupying the largest bandwidth among the media streams. Meanwhile, data prioritizing can be performed according to packets, frames, and objects by the priority packetization unit 110.
FIG. 2 shows a parsing scheme and a data-prioritizing scheme using an MPEG-2 program stream (PS) 210.
The MPEG-2 PS 210 is formed based on a pack 220. The pack 220 includes I packets, an I/P packet, a P/B packet, B packets, an audio packet, and a control packet, which are packetized elementary streams (PESs) having variable sizes. In order to prioritize data according to frames, the PES packets included in the pack 220 are separated from each other through parsing 230.
After the parsing 230, the MPEG-2 PS pack 220 is separated into control packets 240, audio packets 242, and video packets 244 divided according to frames. The packets 240 to 244 become transport streams (TSs) 246 through transport-aware packetization that is predetermined according to the priorities of frame types.
Referring back to FIG. 1, packets prioritized by the priority packetization unit 110 have priorities in the order of the I frame, the P frame, and the B frame and then transmitted through the packet dropping unit 120 when the transmission rate control is required according to the feedback information. The output of the packet dropping unit 120 is inputted to an FEC encoder 130 for adaptation transport based on FEC. The FEC encoder 130 performs an adaptive FEC scheme for dynamically adjusting the FEC strength according to network conditions.
The conventional technique allowing the above-mentioned operation employs an adaptive media-streaming scheme in which media streams are transmitted suitably for dynamically-changing network conditions, and general network monitoring is actively or passively performed. Herein, the active network monitoring enables exact measurement of a network state in a case of shortening transmission periods of packets. In this case, the active network monitoring exerts an influence on QoE (Quality of Experience) of a user by increasing the amount of packets in the network. In contrast, in the passive network monitoring for measuring the network state by using user data, since a great amount of data is collected and analyzed, a great amount of system resources is required. Thus, it is difficult to adjust a measurement period or a measurement time duration. Also, the conventional technique cannot be applied to point to multi-point transmission such as broadcasting or multicasting because end-to-end monitoring information is used. Meanwhile, in a differential service (Diff-Serv) domain supporting QoS by allowing only a server to perform network monitoring and network elements such as routers, cannot dynamically perform QoS mapping.